1. Field of the Invention
The present invention relates to a distance detector used for automatic focusing or other purposes in a silver halide film camera, video camera, SVC (still video camera), or the like.
2. Description of the Prior Art
A conventional example of such a distance detector performs distance measurement within a distance measurement area secured along a horizontal line on an image screen of a camera or the like. The relationship between the image screen and the distance measurement area of this distance detector is shown in FIG. 17. In this distance detector, the distance measurement area L1 covers only a portion along a horizontal center line of the image screen 10, and therefore it is impossible to perform distance measurement with a subject 15 located in an upper and lower portion of the image screen 10.
To achieve distance measurement without fail, some distance detectors employ a distance sensor composed of a plurality of pairs of line sensors, and others even employ an area sensor. In a distance detector of the former type, for example as shown in FIG. 18, distance measurement is performed in distance measurement areas L1 to L5 secured along a plurality of lines, and thus in a wider area in total. Here, the greater the number of distance measurement areas L1 to L5 covered by the individual line sensors, the more likely the subject distance is detected successfully. In addition, measuring the subject distance by the use of a plurality of line sensors leads to higher distance measurement accuracy.
This type of distance detector employs a distance sensor having, for example as shown in FIG. 19, five pairs of line sensors 90 to 94. Each of these pairs of line sensors 90 to 94 has light-sensor arrays 22, which generate photoelectric charges in accordance with the amount of light they receive, and processor arrays 21, which feed out those photoelectric charges successively pixel by pixel. The distance sensor also has, along its vertical center line, a control circuit 20, which generates a clock in synchronism with which the above photoelectric charges are fed out. Conventionally, as shown in FIG. 19, the five pairs of line sensors 90 to 94 are arranged with their light-sensor and processor arrays oriented identically and with the light-sensor arrays spaced evenly.
However, this distance sensor, precisely because it has an increased number of distance measurement areas, requires an accordingly large-scale circuit to control the line sensors, and thus suffers from its comparatively large size. Moreover, the resulting increase in the amount of data to be processed requires that a microcomputer or the like take an unduly long time to calculate the subject distance. This causes a time lag in distance measurement, and thus, in a camera or the like, causes an undesirable delay in automatic focusing, such as may make the operation of the camera uncomfortable.
In particular, in a camera provided with a variable-magnification optical system that can vary the shooting magnification, even if the distance measurement areas L1 to L5 are, as shown in FIG. 20A, so arranged as to evenly cover the entire image screen 10 at a low shooting magnification, as the shooting magnification is increased, the angle of view becomes narrower as shown in FIG. 20B, and thus the distance measurement areas L1 to L5 become more and more widely spaced, until eventually, in some cases, the measurement areas other than the central one L3 go out of the image screen 10. This cannot be said to be an effective increase in the number of distance measurement areas, but rather makes subject-distance measurement less secure.
On the other hand, in a distance detector of the latter type that employs an area sensor, as shown in FIG. 21A, the sensing area of the area sensor is divided into nine equally sized distance measurement areas E1 to E9, and detection of the subject 15 and measurement of the distance to the subject 15 are performed in each of these distance measurement areas E1 to E9.
However, also in this case, distance measurement is performed in accordance with the data obtained from the entire sensing area, and thus the resulting increase in the amount of data to be processed requires that the microcomputer take an unduly long time to calculate the subject distance. Moreover, in a camera provided with a variable-magnification optical system, as shown in FIG. 21B, as the shooting magnification is increased, the distance measurement areas other than the central one E5 go out of the image screen 10. This cannot be said to be an effective increase in the number of distance measurement areas.